NGINX stat() failed error (13: Permission denied)

Encountering errors while using NGINX can be a frustrating experience for any system administrator or developer. One common issue is the stat() failed (13: Permission denied) error. This error indicates that NGINX does not have the necessary permissions to access certain files or directories essential for it to serve content. This guide will explore the causes of this error and present solutions to resolve it effectively.

Solution 1: Check User and Group Settings

The NGINX processes must run as an appropriate user that has read access to the content it’s attempting to serve. By default, NGINX runs as the ‘nginx’ user or ‘www-data’ on some systems. If the files it’s trying to access are not readable by this user, you’ll encounter the permission denied error.

1. Identify the user that NGINX is running as by inspecting the NGINX configuration file, usually located at /etc/nginx/nginx.conf.
2. Check the file permissions of the directory and files that are yielding the error. This can be done using ls -l /path/to/the/files.
3. If the permissions are incorrect, use chown and chmod to set the appropriate owner and read permissions. For example:
   sudo chown -R nginx:nginx /path/to/the/files
sudo chmod -R 755 /path/to/the/files
4. Reload the NGINX configuration to apply changes with the command:
   sudo nginx -s reload.

These are system commands. Verification happens through successful access to resources by NGINX without errors.

Notes: This is often the easiest issue to fix, but it requires access to the server’s file system. Keep in mind that setting permissions too broadly (e.g., 777) can be a security risk. Always set the minimum permissions necessary for NGINX to function.

Solution 2: Check SELinux Contexts

If you’re running NGINX on a system with SELinux enabled, you might face permission issues due to SELinux security contexts. SELinux contexts define how processes and files interoperate under security policies.

1. Check current SELinux file contexts with:
   ls -Z /path/to/the/files
2. To adjust the context so that NGINX can access the files, use the chcon command or use semanage fcontext to persist changes across reboots:
   sudo chcon -R -t httpd_sys_content_t /path/to/the/files
   or
   sudo semanage fcontext -a -t httpd_sys_content_t '/path/to/the/files(/.*)?'
sudo restorecon -Rv /path/to/the/files
3. Verify the new contexts with ls -Z.
4. Try accessing the content through NGINX again.

This is a process of changing security contexts. Verification occurs if NGINX serves content without throwing errors.

Notes: Modifying SELinux policies and contexts should be done with caution to not unintentionally weaken your system’s security posture. Such changes require root or equivalent privileges.

Solution 3: Validate NGINX Configuration File

The issue might also be caused by misconfigured NGINX settings. The error might not be with permissions on the filesystem but with the way that NGINX is trying to access resources.

1. Open the NGINX configuration file using a text editor:
   sudo nano /etc/nginx/nginx.conf or another file if you have a custom configuration.
2. Verify that directives such as root and index are correctly specified and that they point to the right location.
3. Check for server block specific permission settings and ensure that they do not conflict with the global settings.
4. After making any necessary changes, test the configuration using sudo nginx -t.
5. If the test passes, reload the NGINX configuration:
   sudo nginx -s reload.

This is a validation of configuration effectiveness through the test command and server operation.

Notes: A well-validated configuration file is crucial for avoiding various errors not limited to permissions. This approach ensures that NGINX is orchestrated to find and serve files correctly, adhering to best practices for server block management.

Closing Thoughts

Permission denied errors can derail web server functionality but are commonly the result of simple misconfigurations or permission settings. Systematically checking these elements often resolves the issue. Professionals should always be mindful of the security implications when adjusting permissions and settings on a web server, working to balance functionality with a strong security stance.